William W. L. Glenn

Diaphragm Pacing by Electrical Stimulation of the Phrenic Nerve

&NA; Sophisticated techniques for electrical stimulation of excitable tissue to treat neuromuscular disorders rationally have been developed over the past 3 decades. A historical review shows that electricity has been applied to the phrenic nerves to activate the diaphragm for some 200 years. Of the contemporary methods for stimulating the phrenic nerve in cases of ventilatory insufficiency, the authors prefer stimulation of the phrenic nerve in the thorax using a platinum ribbon electrode placed behind the nerve and an attached subcutancously implanted radiofrequency (RF) receiver inductively coupled to an external RF transmitter. Instructions are given for implanting the electrode‐receiver assembly, emphasizing atraumatic handling of the phrenic nerve and strict aseptic techniques. Diaphragm pacing is conducted with low frequency electrical stimulation at a slow repetition (respiratory) rate to condition the diaphragm muscle against fatigue and maintain it fatigue‐free. Candidates for diaphragm pacing are those with ventilatory insufficiency due to malfunction of the respiratory control center or interruption of the upper motor neurons of the phrenic nerve. In the Yale series, there were 77 patients treated by diaphragm pacing; 63 (82%) started before 1981 and thus were available for follow‐up for at least 5 years; 33 (52%) were paced for 5 to 10 years, and 15 (24%) were paced for 10 to 16. Long term stimulation of the phrenic nerves to pace the diaphragm is an effective method of ventilatory support in selected cases. (Neurosurgery 17:974‐984, 1985)

Ventilatory Support by Pacing of the Conditioned Diaphragm in Quadriplegia

Abstract We provided full-time ventilatory support In five patients with respiratory paralysis accompanying quadriplegia by continuous electrical pacing of both hemidia-phragms simultaneously for 11 to 33 months through the application to the phrenic nerves of a low-frequency stimulus. The strength and endurance of the diaphragm muscle increased with pacing. Biopsy specimens taken from two patients who had uninterrupted stimulation for 6 and 16 weeks showed changes suggestive of the development of fatigue-resistant muscle fibers. When we compared these results with those of our earlier experience with intermittent unilateral stimulation of the diaphragm in 17 patients with respiratory paralysis, we found that continuous bilateral pacing using low-frequency stimulation appeared to be superior because of more efficient ventilation of both lungs, fewer total coulombs required to effect the same ventilation, and absence of myopathic changes in the diaphragm muscle. For patients with respiratory paralysis and ...

Total Ventilatory Support in a Quadriplegic Patient with Radiofrequency Electrophrenic Respiration

Abstract A patient with respiratory paralysis from injury of the cervical cord was freed from dependence upon a mechanical respirator through the use of electrical stimulation of both phrenic nerves. This was accomplished with radiofrequency transmission to two radio receiver electrode assemblies implanted subcutaneously 14 months ago. By forceful contractions of his unparalyzed neck muscles the patient is able to assist ventilation voluntarily but is unable to support adequate ventilation by voluntary effort alone for more than a few minutes. Total ventilatory support by radiofrequency electrophrenic respiration has been maintained for more than 11 months. The two sides of the diaphragm are stimulated alternately for periods of 12 hours. Normal tidal volume and blood gas concentration with the patient in the recumbent position have been demonstrated. The tracheostomy tube has been removed; the patient can speak, and he has resumed some normal activities.

Long-term ventilatory support by diaphragm pacing in quadriplegia.

Thirty-seven quadriplegic patients with respiratory paralysis were treated by electrical stimulation of the phrenic nerves to pace the diaphragm. Full-time ventilatory support by diaphragm pacing was accomplished in 13 patients. At least half-time support was achieved in 10 others. There were two deaths unrelated to pacing in these two groups. Fourteen patients could not be paced satisfactorily, and 8 of these patients died, most of them from respiratory infections. The average time the 13 patients on total ventilatory support have had bilateral diaphragm pacemakers is 26 months. The longest is 60 months. Many of these patients are out of the hospital and several are in school or working. Injury to the phrenic nerves either by the initial trauma to the cervical cord or during operation for implantation of the nerve cuff was the most significant complication. Nerve damage from prolonged electrical stimulation has not been a problem thus far. A description of the pacemaker, the technique of its implantation, and the pacing schedule are reported.

Portal hypertension and bleeding esophageal varices; their occurrence in the absence of both intrahepatic and extrahepatic obstruction of the portal vein.

THERE are a few well documented cases of bleeding from ruptured esophageal varices in the absence of associated portal hypertension.1 2 3 However, most patients with life-threatening hemorrhage fro...

Circulatory Bypass of the Right Side of the Heart

Abstract Evidence has been presented to demonstrate that in the dog at least 80 to 85% of superior vena caval flow continues to pass through a cava-pulmonary artery shunt for 81 months postoperative. Collateral flow to the inferior vena cava does not progressively increase and is primarily through the pericardiophrenic veins, although other collateral pathways probably participate to a lesser extent. Morphological examination of the pulmonary vasculature following a cava-pulmonary artery shunt reveals evidence of diffuse and focal increase in bronchial artery supply to the lung, with evidence of perfusion of alveolar capillaries by these vessels. This increase in bronchial circulation is due to a decrease in the blood pressure and volume of pulmonary artery flow following cava-pulmonary artery anastomosis, with a functional result analogous to pulmonary stenosis. These changes were most marked where the azygos vein was left open.

Fundamental considerations in pacing of the diaphragm for chronic ventilatory insufficiency: A multi-center study

Records were reviewed of 477 patients who had diaphragm pacemakers implanted for treatment of chronic hypoventilation. Three groups were established for comparison. (1) Center group: 165 patients operated on in six medical centers participating in a cooperative study; (2) Noncenter group, sufficient data available: 203 patients operated on by surgeons with experience limited to a few cases; (3) Nonstudy group, minimal data available: 109 patients operated on as in group 2; vital statistics only were contributed. The protocol for data gathering was comprised of 154 major variables. Basic data on age, sex, diagnosis and etiology were analyzed for homogenicity of data among the groups. A comprehensive analysis of the pacing methods, complication and results fom the Center group yielded information on the early experience with diaphragm pacing important to its future application.

Long‐Term Follow‐Up of Pacing of the Conditioned Diaphragm in Quadriplegia

ELEFTERIADES, J.A., et al.: Long‐Term Follow‐Up of Pacing of the Conditioned Diaphragm in Quadriplegia. The authors have previously shown that conditioning of the diaphragm for continuous bilateral pacing is a feasible and effective means of ventilation in patients with complete respiratory paralysis from high cervical (above C3) quadriplegia. The present study reports the long‐term results of continuous diaphragmatic pacing. Twelve quadriplegia patients underwent bilateral phrenic nerve pacemaker placement and diaphragm conditioning from 1981 to 1987. Pacing was initiated at 11 Hz and progressively decreased to 7.1 Hz. A pulse train duration of 1.3 seconds for adults and 0.9 seconds for children was used. Long‐term follow‐up information obtained included pacing status (full‐time, part‐time, or mechanical ventilation), ventilation parameters, and social circumstances. Of the 12 patients, 6 continued to pace full time (mean 14.8 years); all were living at home. Three patients paced for an average of 1.8 years before stopping; two were institutionalized. One patient who paced full time for 6.5 years before lapsing to part time, lived at home. Two patients were deceased; one paced continuously for 10 years before his demise, the other stopped pacing after 1 year. Patients who stopped full‐time pacing did so mainly for reasons of inadequate social or financial support or associated medical problems. All patients demonstrated normal tidal volumes and arterial blood gases while pacing full time. Despite theoretical concerns about long‐term nerve damage, no patient lost the ability to pace the phrenic nerve. Threshold currents did not increase over time (original/follow‐up: 0.46/0.47 for right, 0.45/0.46 for left), nor did maximal currents (original/follow‐up: 1.16/1.14 for right, 1.37/1.26 for left). This follow‐up confirms that quadriplegic patients are able to meet long‐term, full‐time ventilation requirements using phrenic nerve stimulation of the conditioned diaphragm. Careful review of diaphragmatic pacing candidates with respect to associated medical conditions, social support, and motivation is essential for appropriate patient selection and successful long‐term results.

Combined central alveolar hypoventilation and upper airway obstruction. Treatment by tracheostomy and diaphragm pacing.

Abstract Long-term pacing of the diaphragm by electrical stimulation of the phrenic nerve has been successfully employed since 1966 in the treatment of patients with alveolar hypoventilation of central origin. Patients were selected for pacing on the basis of arterial blood gas levels indicating hypoventilation, abnormal ventilatory responses to hypercapnia and hypoxia, and characteristic clinical features. The coexistence of central alveolar hypoventilation and sleep-associated upper airway obstruction was detected in 14 patients. Recordings of several physiologic parameters were made during sleep to monitor changes in ventilatory function. Periodic apnea was observed in all patients. Three types were identified: apnea of central origin, that due to upper airway obstruction or a combination of the two. Pacemaker related apneas were also noted. Pacing the diaphragm eliminated apnea of central origin, accentuated apnea due to upper airway obstruction and, in two patients, both of whom had prolonged episodes of central apnea, pacing induced upper airway obstruction. Tracheostomy was performed for the relief of upper airway obstruction in 13 patients. Abnormal ventilatory responses to hypercapnia and hypoxia persisted in five of six patients studied. Of 12 patients studied after tracheostomy nine continued to show marked hypoventilation during sleep and three showed only mild hypoventilation; nocturnal pacing is being continued in these three patients to prevent a recurrence of alveolar hypoventilation. Our studies indicate that upper airway obstruction frequently accompanies central alveolar hypoventilation; the determination of their relative importance requires a ventilatory control study and a carefully monitored sleep study. In patients with combined central alveolar hypoventilation and upper airway obstruction whose condition is resistant to medical therapy, combined tracheostomy and diaphragm pacing are indicated.

GRAFT OF THE DIAPHRAGM AS A FUNCTIONING SUBSTITUTE FOR THE MYOCARDIUM. AN EXPERIMENTAL STUDY.

Summary A segment of diaphragm has been investigated as a potential myocardial graft. The specific operative technique assured maintenance of the segments blood and nerve supply. Innervation of the graft via the phrenic nerve was essential for preservation of muscular structure and contractility. The contractile force of the graft, measured by a strain gauge arch at various times after graft transplantation, showed no significant change from that measured in the fresh state. Functional integrity of the graft transplanted to the right atrium could be demonstrated for prolonged periods after transplantation. Synchronization of phrenic nerve stimulation with systole resulted in augmentation of cardiac contraction as evidenced by a rise in blood pressure.